Diatomaceous earth filteraid and method for its manufacture

ABSTRACT

A method is provided for treating diatomaceous earth filteraids having a beer-soluble iron content of less than about 0.01% to further reduce the beer-soluble iron content by maintaining the filteraids in contact with a relatively small volume of an acid. In the filteraids so produced, the beer-soluble iron content can be reduced by as much as 70% to 100%. In making the filteraids of this invention, sulfuric acid in about 0.1 to about 3.0 normal solution can be used to treat the starting filteraids.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 849,873, filed Nov. 9,1977, now issued as U.S. Pat. No. 4,142,968.

This invention relates to the manufacture of diatomaceous earthfilteraids. More specifically, this invention relates to a method ofreducing the beer-soluble iron content of diatomaceous earth filteraidsand the filteraids produced thereby.

BACKGROUND OF THE INVENTION

Diatoms are microscopic, unicellular aquatic plants which aredistinguished by an opaline silica shell. Upon dying, the diatoms sinkto the bottom of the water and the shells form a bed which may beseveral hundreds of feet thick. These beds may eventually elevate abovethe surrounding water level, and through prolonged and repeatedleaching, become purified. Material from these beds is calleddiatomaceous earth or diatomite.

The remarkable properties of diatomaceous earth make it industriallyuseful. Its inertness and various shapes make it an excellent filteraidand as such it is used extensively throughout the world.

In filteraid manufacture, diatomaceous earth is mined by the open quarrymethod, transported to a mill, crushed, screened, and put into storagebins. Material from these bins is dried, extraneous material such asclay and chert is removed, and the diatomaceous earth ore is thencalcined in a rotary kiln. After calcining the filteraid is milled,classified, bagged, and shipped to the customer.

Filteraids are generally divided into two types according to the methodof calcination. In one method, straight calcining, milled diatomite fromthe storage bins is passed through a rotary calciner. The resultingproducts are called "pinks" or calcined diatomaceous earth. In the othermethod, flux-calcining, the purified crude from the storage bin is mixedwith a flux, usually sodium carbonate, and passed through a rotarycalciner. The resulting products are called "whites" or flux-calcineddiatomaceous earth. Both white and pink filteraids are used extensivelyin the brewing and pharmaceutical industries.

Diatomaceous earth filteraid materials normally contain iron in variousforms, one or more of which may be soluble in the liquid being filtered.In the brewing of beer, for example, the beer is preferably clarified byfiltering through diatomaceous earth filteraid material. However, theiron content of the normal filteraids which is soluble in beer has adeleterious effect on the beer.

The presence of iron in beer is widely known. W. P. K. Findlay, ModernBrewing 256 (1971) establishes that the presence of iron in beer inexcess of several micrograms per gram can cause a severe decline instability or shelf life. Similarly, soluble iron affects the stabilityof various pharmaceuticals and distilled spirits. C. J. King, SeparationProcesses 18 (1971). Reduction of beer-soluble iron in diatomaceousearth filteraids prolongs the shelf life of the beer.

In view of the value of the diatomaceous earth filteraids in theclarification of beer in the brewing process, there has been a greatdeal of interest over a long period of time in economical and efficientways and means for removing the beer-soluble iron from the filteraidmaterial or changing the form of the iron content so as to render itsubstantially insoluble in beer.

It was discovered, for example, that by some internal chemical process,a certain percent of the beer-soluble iron becomes insoluble to thebeer, merely by the aging of the filteraids before use in the brewingprocess. During aging of the filteraid for approximately one month, upto 20% of the beer-soluble iron may be rendered beer-insoluble.

U.S. Pat. No. 665,652 to Enzinger describes a process for producing adiatomaceous filteraid useful for filtering beer. The diatomite isheated in an aqueous solution of twenty percent hydrochloric acid andone percent nitric acid for some hours in an autoclave at a temperatureof about 120° C. The steps of filtering, washing and pressing follow.However, the process fails to reduce beer-soluble iron to the extremelylow levels sufficient to meet the more sophisticated demands of today'sbeer producer.

Without focusing specifically on the reduction of beer-soluble ironcontent, others have sought to reduce water and acid-soluble ironcontents of diatomaceous earth filteraids. U.S. Pat. No. 2,701,240 toBregar discloses a process to reduce acid-soluble iron content indiatomite filteraids from about 3 percent to less than 0.02 percent,with one example reporting reduction to 0.005 percent. The processincludes flux-calcining followed by contacting with acid, heating andagitating from fifteen minutes to several hours, filtering, preferablywashing, drying and sometimes milling. Preferably, excess of acid isemployed. The examples in the Bregar specification indicate that theamount of acid used is about 600 percent by weight based on dryfilteraid weight. The process does not employ calcined diatomaceousearth filteraids.

U.S. Pat. No. 1,992,647 to Schuetz describes a method of producing adiatomaceous earth filteraid with less than 0.03% water-solublematerial. The preferred embodiment of the process includes treatingcomminuted, but not calcined, diatomaceous earth with a strong mineralacid, suitably sulfuric acid, leaching with water, drying, milling,calcining, treating with a dilute mineral acid, leaching, drying andmilling.

All of these prior art methods fail to reduce beer-soluble content indiatomaceous earth filteraids to the extremely low levels desired in thebrewing industry. Further, the methods involve either processing for aconsiderable period of time or otherwise complicated and expensiveprocedure. Most of the methods also employ leaching processes to removeimpurities.

Accordingly, a primary object of the present invention is to efficientlyand economically reduce beer-soluble iron in diatomaceous earthfilteraids to an extremely low level to meet the more sophisticateddemands of today's beer producer.

A further object is to provide a process of adding small quantities of adilute acid solution to the filteraid to tie-up the beer-soluble ironrather than to remove it. The fact that the small residual acid used isallowed to stay with the product further reduces the processing cost.

SUMMARY OF THE INVENTION

These and other objects which will become apparent hereinafter areachieved by the present invention which provides a method for producingdiatomaceous earth filteraids with greatly reduced levels ofbeer-soluble iron comprising the steps of mixing diatomaceous earthfilteraids having an initial beer-soluble iron content of less thanabout 0.01% or 100 parts per million with a volume of aqueous acidsolution sufficient, but preferably not in excess, to wet the filteraidsuniformly and then maintaining the acid in contact with the filteraidfor a period of time sufficient to reduce the beer-soluble iron contentof the filteraid. The acid used is one which reduces beer-soluble ironcontent within seven days when applied as a 3.0 normal aqueous solutionto a diatomaceous earth filteraid in an amount of 15% by weight based onthe weight of the dry filteraid.

Preferably, the acid used is sulfuric acid having a relatively low acidconcentration and is used in relatively small volume. The minimum amountof acid required to obtain a satisfactory reduction in the beer-solubleiron is in the order of magnitude of about 4 gram equivalents per ton offilteraid. It is preferred that the small amount of acid remaining atequilibrium is allowed to stay with the filteraid to reduce theprocessing costs.

Therefore, such expensive and time consuming steps as leaching, washingand drying may be avoided. Alternatively, the filteraids may be dried.Rather than leaching to remove impurities, the present process involvesutilizing an acid to tie-up the iron and/or render it inactive.

The diatomaceous earth filteraids produced by this process are importantin many industries, particularly the brewing and pharmaceuticalindustries, where soluble iron has a detrimental effect on product shelflife.

With certain acids, the beer-soluble iron content of the flux-calcineddiatomaceous earth filteraids employed in this process isinstantaneously reduced from 70% to 100%. During the course of reaction,the filteraid may be packaged and shipped to the customer.Alternatively, the filteraid may be dried almost immediately in apneumatic or rotary dryer or some other commercial drying equipment andthen packaged and shipped to customers.

In the case of calcined diatomaceous earth filteraids, the processrequires about two weeks to reduce the beer-soluble iron content from30% to 40%. The filteraid may be packaged and warehoused during thistime and then shipped to the consumer.

The present invention consists of the processes and articles set forthherein and in the appended claims. It is to be understood that both theforegoing general description and the following detailed descriptionsare exemplary and explanatory, but are not restrictive of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, and as embodied herein, thereis provided a method including the steps of mixing diatomaceous earthfilteraid of a beer-soluble iron content less than about 0.01% with avolume of aqueous acid solution sufficient, but not in excess, to wetthe filteraids uniformly and maintaining the acid in contact with thefilteraids for a period of time sufficient to reduce the beer-solubleiron content of the filteraid.

Both flux-calcined and calcined diatomaceous earth filteraids may beemployed as starting materials. As mentioned earlier, calcined diatomitefilteraids are obtained by passing milled diatomite through a rotarycalciner. Preferably, flux-calcined filteraids are used. To produceflux-calcined diatomite filteraids, the purified crude from the storagebin is mixed with a flux, usually sodium carbonate, and passed through arotary calciner.

This invention employs as a starting material diatomaceous earthfilteraids with a beer-soluble iron content of less than about 0.01% or100 parts per million. Preferably, the beer-soluble iron content is lessthan 0.005% or 50 parts per million. Flux-calcined or calcined diatomitefilteraids of these levels of beer-soluble iron may be obtained byconventional techniques as described above.

For example, commercially available flux-calcined diatomaceous earthfilteraids of the type "Dicalite Speedex" and "Dicalite Speedplus," andcalcined diatomaceous earth filteraids of the type "231" may be used.

In keeping with the concept of the invention, the starting diatomaceousearth filteraids are wetted with an aqueous acid solution of a suitableinorganic or organic acid. A suitable acid is one which reducesbeer-soluble iron content in seven (7) days when applied as a 3.0 normalaqueous solution to a diatomaceous earth filteraid in an amount of 15%by weight based on the weight of the dry filteraid.

In general, suitable acids will be moderately strong or strong inorganicor organic acids. Preferably, the acid is an inorganic acid, especiallyone chosen from the inorganic acid group consisting of sulfuric acid,hydrochloric acid, and nitric acid. Most preferably, the acid solutionis sulfuric acid. Suitable organic acids include acetic acid and oxalicacid.

One of the advantages of the present invention is that a concentratedacid solution is not required. In general, a relatively dilute solutionis used in the practice of this invention. A suitable concentration ofacid solution is at least in the order of magnitude 0.1 normal and,preferably, the concentration range is between about 0.2 normal andabout 3.0 normal. About 1.0 normal is most preferred.

Another advantage of this invention is that large quantities of acid arenot needed to reduce the beer-soluble iron content. The amount should beonly that which is sufficient to evenly wet the filteraids. A suitableamount of acid solution is from about 2% to about 15% by weight based ondry filteraid weight. Alternatively expressed, this is from about 4 toabout 400 gram equivalents of acid per ton of dry filteraid. Thepreferred amount of acid solution is 4% by weight based on dry filteraidweight.

To treat the filteraids, they are mixed with the relatively dilutesolution of acid. Mixing may be accomplished by any suitable means, suchas by the use of a ribbon blender.

The temperature at which the filteraids and the acid solution are mixedmay be between room temperature and the boiling point of the acidicsolution. Preferably, the mixing is accomplished at room temperature.

After mixing, the filteraids and the acid solution are maintained incontact for a time sufficient to reduce the beer-soluble iron content tothe desired level. It is believed that the acid reacts or complexes withthe iron to render it beer-insoluble since the reduction in beer-solubleiron content has been found to occur without leaching or washing. By theprocess of this invention, reduction of beer-soluble iron content canbegin to occur almost immediately upon mixing the filteraids with theacid solution.

It has been found that with flux-calcined filteraids, a substantialreduction in beer-soluble iron content can occur instantaneously. Ingeneral, the reduction occurs over a period of from about one to about 5hours. It has been found that the mixing can occur in the plant processjust prior to the bagging operation. After mixing, the product is fed tothe packer and bagged in the normal manner, with the net result being nochange or interruption of the plant operation. Alternatively, thefilteraids and acid solution are maintained in contact until thereaction reaches equilibrium. Flux-calcined filteraids are the preferredstarting material.

For calcined diatomite filteraids, it is found that substantialreduction occurs in about seven to about fourteen days, usually in aboutfourteen days.

Generally, the small residual acid remaining may be allowed to stay withthe filteraid. Since merely maintaining the acid solution and filteraidsin contact, without continuous leaching or washing, achieves thereduction of beer-soluble iron content in accordance with the presentinvention, the filteraids wetted with acid solution can be packaged andstored for subsequent use or shipment, the reaction occurring withoutany further processing.

Alternatively, flux-calcined filteraids may be dried, such as in apneumatic or rotary dryer, and then stored for subsequent use orshipment.

The following examples, in conjunction with the general and detaileddescription above, more fully illustrate the nature and character of thepresent invention. The examples are illustrative only and are notintended to limit the scope of the invention.

EXAMPLE 1

Flux-calcined diatomaceous earth filteraids of the grade "Speedex"having a beer-soluble iron content of less than 0.005% or 50 parts permillion were mixed at room temperature in accordance with this inventionwith 7% solutions of 0.19 normal hydrochloric acid (Run 1) and 0.38normal hydrochloric acid (Run 2) and beer-soluble iron content wasmonitored over a period of 35 days. The beer-soluble iron content wasimmediately reduced substantially in each case.

For comparison, the filteraids were mixed and maintained in contact atroom temperature with 7% solutions of water (Run 3) and of 1 normalsodium hydroxide (Run 4). The effect on beer-soluble iron content of thewater and basic solution treatments was significantly inferior to theacid treatments.

The results of the four runs of this Example are set forth below inTable I. Beer-soluble iron content is in parts per million.

                  TABLE I                                                         ______________________________________                                                           Beer-Soluble Iron Content                                  Run                Day                                                        No.  Treatment     0      1    7    14   21   35                              ______________________________________                                        1    7% .19 Normal HCl                                                                           41.2   12.8 13.2 16.0 --   16.0                            2    7% .38 Normal HCl                                                                           39.2    4.4  3.2  3.6 6.8   8.0                            3    7% H20        40.0   36.0 32.0 30.8 29.2 25.2                            4    7% Normal                                                                     NaOH          40.0   65.5 51.2 28.8 --   --                              ______________________________________                                    

The beer-soluble iron concentrations were determined in Schlitz beerusing the American Society of Brewing Chemists' standard test method No.B-13, 11/6/72, Beer Soluble Iron In Filteraid. It is described asfollows:

Scope

This is a colorimetric method for determination of beer-soluble iron infilteraids. Extraction is according to the American Society of BrewingChemists--Filteraids-4, "Iron Pick-up by Beer". The iron is detected bythe orange-red color developed by the addition of 1,10 phenanthroline,ASBC-Beer-18, "Iron".

Reagents & Equipment

1. FerroVer powder, 1,10 phenanthroline.

(Cat. No. 303, Hach Chemical Company, Ames, Iowa)

2. Dispenser bottle, 0.1 gram delivery.

(Cat. No. 466, Hach)

3. Standard iron solution. This can be used for STM A-1. It contains0.000143 gms. of Fe₂ O₃ or 0.1 mg. Fe/cc or 100 ppm Fe. Color standardsrepresenting an iron pick-up in beer of 0.1, 0.25, 0.5, 1.0, 1.5, 2.0,2.5, 3.0 ppm Fe are prepared with degassed beer and read at 505 mu vs. abeer blank set at 100% transmittance. The readings are plotted onsemi-logarithmic (2 cycle×70 divisions) with % transmittance onlogarithmic scale vs. ppm Fe pick-up in beer. This calibration should bechecked whenever the instrument is repaired and/or once every 4 months.

4. Iron standard--HachVer--Cat. No. 908. One pillow in 25 mls. degrassedbeer yields a 1.0±0.1 ppm solution of iron as Fe. These have proven tobe excellent for fast checks on the instrument calibration betweenchecks with the standard iron solution. Our work indicates results areaccurate within ±0.05 ppm Fe.

5. Degassed bottled beer (we use Schlitz).

6. Bausch & Lomb Spectronic 200 calibrated at 505 mu for beer basestandards. Curve sensitivity should be controlled to between 20% and 80%transmittance for accuracy.

7. Glass funnel, 60°, 125 mm. diameter.

8. Filter paper, 25 cm. in diameter, E & D 613, Whatman No. 1 or S and SNo. 602.

9. Stop watch.

Procedure: (A) Extraction

Adjust the temperature of 200 mls. of decarbonated beer in a 1000 ml.Erlenmeyer flask to 75° F. (room temperature). Add 5.0 grams offilteraid to the beer and start a stop watch at the moment of addition.Swirl the flask to put all of the filteraid into suspension. Allow thefilteraid to settle and swirl the flask again at 1, 2, 3, 4, and 5minutes of elapsed time, allowing the filteraid to settle after eachswirling. Swirl the flask again at 5 minutes and 50 seconds, andimmediately transfer the entire suspension to a funnel fitted with aniron-free filter paper.

Discard the filtrate collected during the first 30 seconds. Collectfiltrate in a clean beaker for the next 150 seconds and determine theiron content of the filtrate as in B below. Also treat 200 mls. of beerwithout filtraid in the same manner for use as the instrument blank.

(B) Iron Determination

1. B & L Spectronic 20 is calibrated at 505 mu from 0 to 3 ppm Fe/unit(1 ml.) vs % transmittance. Beer blank must be used for 100%transmittance sample in all testing.

2. Measure 25 mls. of sample in a graduated cylinder and pour into aclean 125 Erlenmeyer flask or 100 ml. Griffin beaker.

3. Add 0.1 grams (one measure from the dispensing bottle) of FerroVer tothe sample. Swirl to mix. Let the sample stand for 2 minutes, but nolonger than 5 minutes before comparing color. Keep samples out of directsunlight.

4. Measure the color by reading transmittance of the sample using a 1/2"B & L photometric test tube. This gives a chart reading in ppm Fepick-up/ml. of beer.

5. To obtain the amount of beer-soluble iron in 5 gms. of filteraid in200 mls. of beer, you must multiply the reading×40. Thus, 0.8 ppm Fe(reading)×40=32 ppm (0.032 mg.) beer soluble iron in the filter aidsample.

EXAMPLE 2

Calcined diatomaceous earth filteraids of the grade "231" having abeer-soluble iron content of 0.0016%, i.e., 16 parts per million, weremixed, in accordance with this invention, with a 7% solution of 0.38normal hydrochloric acid (Run 1) at room temperature and beer-solubleiron content was monitored for fourteen days. Notwithstanding the lowstarting level of the beer-soluble iron content, this treatment resultedin a reduction of the beer-soluble iron content.

For comparison, the filteraids were mixed and maintained in contact atroom temperature with 7% solutions of water (Run 2) and of 1 normalsodium hydroxide (Run 3). The water treatment was not as effective asthe acid treatment, and the treatment with basic solution actuallycaused a substantial increase in beer-soluble iron content.

The results of the three runs of this Example are set forth below inTable II. Beer-soluble iron content is in parts per million, and themethod for beer-soluble iron content measurement is the same as was usedin Example 1.

                  TABLE II                                                        ______________________________________                                                           Beer-Soluble Iron Content                                  Run                Day                                                        No.  Treatment     0      1    7    14   21   35                              ______________________________________                                        1    7% .38 Normal HCl                                                                           14.8   14.8 13.2  9.6 --   --                              2    7% H.sub.2 O  16.0   16.0 14.0 14.0 12.0 11.2                            3    7% 1 Normal                                                                   NaOH          16.0   100.4                                                                              48.0 48.4 --   --                              ______________________________________                                    

EXAMPLE 3

The effect of mixing various acids with the filteraid at roomtemperature was compared to the effect of addition of water and beer. Astarting flux-calcined diatomaceous earth filteraid of the grade"Speedplus" was used in each case. The concentration of each acid was0.5 molar and the amount of acid solution in each case was 4% by weightbased on dry filteraid weight. The value of beer-soluble iron in thefilteraid was measured at six days and at thirty-six days. Thebeer-soluble iron content measurement was the same as was used inExample 1 except that beer-soluble iron was measured in Budweiser beerrather than in Schlitz beer.

The initial beer-soluble iron content of the filteraid was 42 parts permillion. The results are summarized in Table III. Beer-soluble iron ismeasured in parts per million. While organic acids such as acetic acidand oxalic acid were somewhat effective, others such as tartaric acidand citric acid actually showed a reverse effect. The reason for this isnot known.

                  TABLE III                                                       ______________________________________                                        EFFECT OF VARIOUS ADDITIVES ON THE BSI OF                                     FLUX-CALCINED D.E. FILTERAIDS                                                                      Beer-Soluble Iron                                        Additive Formula           6 Days   36 Days                                   ______________________________________                                        Sulfuric Acid                                                                          H.sub.2 SO.sub.4   5        7                                        Nitric Acid                                                                            HNO.sub.3         14       18                                        Hydrochloric                                                                  Acid     HCl               15       19                                        Acetic Acid                                                                            CH.sub.3 COOH     15       21                                        Oxalic Acid                                                                            HOOCCOOH--2H.sub.2 O                                                                            21       15                                        Beer     --                34       27                                        Water    H.sub.2 O         35       22                                        Lactic Acid                                                                            CH.sub.3 CHOHCOOH 42       36                                        None                       42       40                                        Boric Acid                                                                             H.sub.3 BO.sub.3  47       45                                        Tartaric Acid                                                                          HOOC(CHOH).sub.2 COOH                                                                           52       44                                        Citric Acid                                                                            HOOC CH.sub.2 C(OH)--                                                         (COOH) CH.sub.2 COOH H.sub.2 O                                                                  94       79                                        ______________________________________                                    

EXAMPLE 4

A series of tests were conducted to determine the most effectivequantity of acid. As starting materials, two different flux-calcineddiatomaceous earth filteraids of grades "Dicalite Speedplus" and"Dicalite Speedex" were utilized.

In the first series of tests, "Speedplus" filteraids were mixed at roomtemperature with amounts of hydrochloric acid solution varying from 2%to about 6% by weight based on dry filteraid weight. The concentrationof the hydrochloric acid solutions varied from 0.10 normal to about 1.5normal For comparison, a test was run using water as the additive. Forfurther comparison, a sample was run to determine the reduction inbeer-soluble iron occurring merely from the passage of time with neitheracid nor water being added.

The amount of beer-soluble iron (represented in Table IV as BSI) wasmeasured four days after treatment by the same method disclosed inExample 1, with the exception that in these tests Budweiser beer wasemployed. There is a slight difference in value depending upon the beerused; however, the relative differences and the effect remains the same.The results are summarized in Table IV. The best results indicate about60% to about 63% reduction in beer-soluble iron content.

                  TABLE IV                                                        ______________________________________                                        EFFECT OF ACID (HCl) QUANTITY                                                 ON BEER-SOLUBLE IRON OF FLUX-CALCINED                                         D.E. FILTERAIDS OF GRADE "SPEEDPLUS"                                          Sample                           %                                            No.    gm Equivalents                                                                              Normal Conc.                                                                              Solution                                     126R-6 Acid Per Ton D.E.                                                                           HCl         Added  BSI                                   ______________________________________                                        IA     0             0           0      44                                    IB     0             0(H20 only) 4      40                                    IC     3.6           0.10        4      40                                    IE     6.7           0.37        2      26                                    ID     7.2           0.20        4      38                                    IF     13.4          0.37        4      17                                    IG     20.2          0.37        6      17                                    IH     26.9          0.74        4      16                                    II     54.5          1.50        4      18                                    ______________________________________                                    

In Table IV, diatomaceous earth is abbreviated D.E. and values of BSIare in parts per million.

A second series of tests were run using the "Speedex" diatomaceous earthfilteraid as a starting material. The filteraids were mixed at roomtemperature with amounts of hydrochloric solution varying from 2% toabout 6% by weight based on dry filteraid weight. The concentration ofthe acid solution varied between about 0.1 normal and about 1.5 normal.Again, comparative tests were run to determine the effect of addition ofwater, without acid, and to evaluate the reduction in beer-soluble ironresulting from the mere passage of time. The amount of beer-soluble iron(represented in Table IV as BSI) was measured five days after treatment.The same method disclosed in Example 1 was utilized to measure thebeer-soluble iron value except that Budweiser rather than Schlitz beerwas used. The results are summarized in Table V. The best resultsindicate about 83% to 100% reduction in beer-soluble iron.

                  TABLE V                                                         ______________________________________                                        EFFECT OF ACID (HCl) QUANTITY                                                 ON BEER-SOLUBLE IRON OF FLUX-CALCINED                                         D.E. FILTERAIDS OF GRADE "SPEEDEX"                                            Sample                           %                                            No.    gm Equivalents                                                                              Normal Conc.                                                                              Solution                                     126R-6 Acid Per Ton D.E.                                                                           HCl         Added  BSI                                   ______________________________________                                        IIA    0             0           0      24                                    IIB    0             0(H.sub.2 O only                                                                          4      18                                    IIC    3.6           0.10        4      17                                    IIE    6.7           0.37        2      12                                    IID    7.2           0.20        4      17                                    IIF    13.4          0.37        4       4                                    IIG    20.2          0.37        6       3                                    IIH    26.9          0.74        4       2                                    III    54.5          1.50        4       0                                    ______________________________________                                    

In Table V, diatomaceous earth is abbreviated D.E. and values of BSI arein parts per million.

In general, the tests summarized in Tables IV and V indicate that theeffectiveness of the acid is proportional to the quantity added. Theminimum amount of acid required to obtain a satisfactory reduction inthe beer-soluble iron appears to be in the order of magnitude of 5 gramequivalents of acid per ton of filteraid. In order to insureeffectiveness, the acid should be added with at least 4% water; forexample, an effective procedure appears to be to mix 4% of a 0.4 normalHCl solution with the diatomaceous earth.

EXAMPLE 5

The commercial viability of the process was tested at the plant level,again using hydrochloric acid. In the first test, flux-calcineddiatomaceous earth filteraid of grade "Dicalite Speedex" was used as astarting material. Hydrochloric acid solution of 0.4 normalconcentration, in an amount 4% by weight based on the dry filteraidweight was mixed with the filteraid. For comparison, a separateexperiment mixing the "Dicalite Speedex" with water in the amount of 4%by weight based on the dry filteraid weight was performed.

The plant test was carried out using a crude homemade mixer (a ribbonblender would be desirable) and a spray manifold with several nozzlesthrough which the water and acid solutions were metered into thefilteraid. The operation was inserted into the plant process just priorto the bagging operation. After mixing, the product was fed to thepacker and bagged in the normal manner. The operation was runcontinuously, thus causing no change or interruption to the plantoperation.

The amount of beer-soluble iron (abbreviated in Table VI as BSI) wasmeasured nineteen days after treatment by the method disclosed inExample 1 with the exception that Budweiser beer was used. The resultsare summarized in Table VI.

                  TABLE VI                                                        ______________________________________                                        PLANT TEST USING ACID TREATMENT TO REDUCE                                     BEER-SOLUBLE IRON OF FLUX-CALCINED                                            DIATOMACEOUS EARTH FILTERAIDS                                                              Dicalite Speedex                                                  Filteraid                   HCl                                              Treatment      Water         Acid                                             ______________________________________                                        Initial BSI    25            25                                               BSI after 19 days                                                                            17             4                                               ______________________________________                                    

The values of BSI are in parts per million. It is observed that an 84%reduction in beer-soluble iron occurred. An identical second test wasrun, with the sole exception that "Dicalite Speedplus" was used as thestarting diatomaceous earth filteraid. The results, summarized in TableVII, indicate a 64.5% reduction in the beer-soluble iron content.

                  TABLE VII                                                       ______________________________________                                        PLANT TEST USING ACID TREATMENT TO REDUCE                                     BEER-SOLUBLE IRON OF FLUX-CALCINED                                            DIATOMACEOUS EARTH FILTERAIDS                                                              Dicalite Speedplus                                                Filteraid                  HCl                                               Treatment      Water        Acid                                              ______________________________________                                        Initial BSI    45           45                                                BSI after 19 days                                                                            29           16                                                ______________________________________                                    

EXAMPLE 6

A series of tests were run to determine the effects of sulfuric acid onbeer-soluble iron of flux-calcined diatomaceous earth filteraids."Dicalite Speedplus" diatomaceous earth filteraid was used as a startingmaterial. The initial concentration of beer-soluble iron in the"Dicalite Speedplus" was 38.8 parts per million. The filteraids weremixed at room temperature with about 4% of about a 1.0 normal sulfuricacid solution. As is summarized in Table VIII, beer-soluble iron contentof samples was measured immediately after mixing, and at one, two,three, four, and five hours after mixing. Sample No. 2 was measuredafter the filteraid had been oven-dried at 300° Fahrenheit for two hoursafter mixing. The amount of beer-soluble iron (represented im Table VIIIas BSI) was measured by the same method disclosed in Example 1 exceptthat Budweiser rather than Schlitz beer was used. The results from TableVIII indicate an instantaneous reduction of about 78% in beer-solubleiron content and a reduction of about 95% after five hours.

                  TABLE VIII                                                      ______________________________________                                        EFFECT OF H.sub.2 SO.sub.4 ON BEER-SOLUBLE IRON                               OF FLUX-CALCINED D.E. FILTERAIDS                                              Sample No.  Time After Mixing  BSI                                            ______________________________________                                        1          Starting Material   38.8                                           2          After Mixing        8.8                                            3          Oven Dried at 300°  F. for                                                                 11.2                                                      2 hours (after mixing)                                             4          One Hour            8.0                                            5          Two Hours           5.2                                            6          Three Hours         3.6                                            7          Four Hours          2.8                                            8          Five Hours          1.6                                            ______________________________________                                    

In Table VIII, diatomaceous earth is abbreviated D.E. and values of BSIare in parts per million.

EXAMPLE 7

A series of tests were run to determine the effect of sulfuric acidconcentration and weight-percent on reduction of beer-soluble ironcontent in diatomaceous earth filteraids. "Dicalite Speedplus"diatomaceous earth filteraid was used as a starting material. Theinitial concentration of beer-soluble iron in the "Dicalite Speedplus"was 38.8 parts per million. The filteraids were mixed at roomtemperature with solutions of sulfuric acid ranging in concentrationfrom about 0.2 normal to about 3.0 normal. The weight-percent of theacid solution, compared to the weight of the diatomaceous earthfilteraid, varied from about 2% to about 15%. As is summarized in TableIX, beer-soluble iron content of the diatomaceous earth filteraids wasmeasured immediately after mixing and also one day after mixing. Theamount of beer-soluble iron (represented in Table IX as BSI) wasmeasured by the same method disclosed in Example 1 except that Budweiserrather than Schlitz beer was used. The best results from Table IX showan instantaneous reduction of about 81% in beer-soluble iron content anda reduction of about 96% after one day.

The results show that reductions in beer-soluble iron content increasein certain ranges as the concentration of acid is increased whileholding constant the weight-percent volume of acid solution added. Inother concentration ranges, at constant weight-percent volume, the useof lower concentrations is more beneficial. A similar observation can bedrawn from the data of Table IV. In general, the amounts andconcentration of acid solution used should optimize economics andresults.

                  TABLE IX                                                        ______________________________________                                        EFFECT OF H.sub.2 SO.sub.4                                                    CONCENTRATION AND WEIGHT-PERCENT                                              ON BEER-SOLUBLE IRON IN D.E. FILTERAIDS                                              Normal                                                                 Sample Concen-  %       gram equivalents                                      No.    tration  Added   Acid per ton DE                                                                          BSI.sup.(1)                                                                         BSI.sup.(2)                          ______________________________________                                        1      0        0       0          38.8  38.8                                 2      0.2      4        7.3       29.2  25.6                                 4      0.4      4       14.5       16.0  13.2                                 6      0.8      4       29.1       15.2  5.6                                  7      1.2      4       43.6       13.2  7.6                                  8      2.0      4       72.6        7.2  5.6                                  10     3.0      4       109.0      42.8  7.2                                  3      0.4      2        7.3       29.2  25.2                                 5      0.4      15      54.5       21.2  4.0                                  9      3.0      2       54.5       24.0  15.6                                 11     3.0      15      408.6      72.0  1.6                                  ______________________________________                                         .sup.(1) Measurement taken immediately after mixing.                          .sup.(2) Measurement taken after one day.                                

In Table IX, diatomaceous earth is abbreviated D.E. and values of BSIare in parts per million.

The preferred embodiment and best mode of this invention presentlycontemplated by me is the mixing of 4% by weight, 1.0 normal solution ofsulfuric acid with flux-calcined diatomaceous earth filteraids of lessthan 0.005% or 50 parts per million beer-soluble iron content. Thefilteraids are evenly wet by the acid solution and the reaction isallowed to proceed. The beer-soluble iron content is thereby reducedfrom 70% to 100%.

The invention in its broader aspects is not limited to the specificembodiments described. Certain modifications will be obvious to thoseskilled in the art and can be executed without departing from the scopeand spirit of the invention and without sacrificing the principaladvantages of the invention.

What is claimed is:
 1. A process for producing diatomaceous earthfilteraids of reduced beer-soluble iron content comprising the steps ofmixing diatomaceous earth filteraids having a beer-soluble iron contentof less than about 0.01% with an amount of aqueous acid solution lessthan about 15% by weight, based on the weight of the dry filteraids, andsufficient, but not in excess, to wet said diatomaceous earth filteraidsuniformly, said acid being one which is capable of reducing saidbeer-soluble iron content within seven days when applied as a 3.0 normalaqueous solution to a diatomaceous earth filteraid in an amount of 15 %by weight based on the weight of the dry filteraid; and maintaining theacid solution in contact with the filteraids for a period of timesufficient to reduce the beer-soluble iron content of said filteraids byat least about 30%.
 2. A process according to claim 1 wherein the amountof acid solution is from about 2% to 15% by weight based on the dryfilteraid weight and the concentration of the acid solution is at leastabout 4 grams equivalents of acid per ton of diatomaceous earthfilteraid.
 3. A process according to claim 1 wherein the concentrationof the acid solution is from about 4 gram equivalents of acid per ton ofdiatomaceous earth filteraid to about 400 gram equivalents of acid perton of diatomaceous earth filteraid.
 4. A process according to claim 1wherein the acid is selected from the group consisting of acetic acidand oxalic acid.
 5. A process according to claim 1 wherein the acid isan inorganic acid.
 6. A process according to claim 5 wherein the acid isselected from the group consisting of sulfuric acid, nitric acid, andhydrochloric acid.
 7. A process according to claim 6 wherein the acid issulfuric acid.
 8. A process according to claim 7 wherein theconcentration of the sulfuric acid solution is from about 0.1 normal to3.0 normal and the amount of said acid solution is from 2% to 15% byweight based on the dry filteraid weight.
 9. A process according toclaim 1 wherein the acid solution is maintained in contact with thefilteraids for a period of time between 0 and about 36 days.
 10. Aprocess according to claim 1 further including the step of drying thefilteraid after contact with the acid solution.
 11. A process accordingto claim 1 wherein the starting diatomaceous earth filteraids have abeer-soluble iron content of less than about 50 parts per million or0.005%.
 12. A process according to claim 1 wherein the startingdiatomaceous earth filteraids are flux-calcined filteraids.
 13. Aprocess according to claim 1 wherein the starting diatomaceous earthfilteraids are calcined filteraids.
 14. A process according to claim 1wherein the aqueous acid solution is mixed and maintained in contactwith the diatomaceous earth filteraids at room temperature.
 15. Aprocess for producing diatomaceous earth filteraids of reducedbeer-soluble iron content comprising the steps of mixing calcineddiatomaceous earth filteraids having a beer-soluble iron content of lessthan about 0.01% with an aqueous acid solution of a strong or moderatelystrong inorganic acid of concentration of at least 4 gram equivalents ofacid per ton of diatomaceous earth filteraid, said aqueous acid solutioncomprising less than about 15% by weight, based on the weight of the dryfilteraids, and in an amount sufficient, but not in excess, to wet saiddiatomaceous earth filteraids uniformly; and maintaining the acidsolution in contact with the filteraids for a period of time sufficientto reduce the beer-soluble iron content of said filteraids by at leastabout 30%.
 16. A process according to claim 15 wherein said inorganicacid is one which reduces beer-soluble iron content within seven dayswhen applied as a 3.0 normal aqueous solution to a diatomaceous earthfilteraid in an amount of 15% by weight based on the weight of the dryfilteraid.
 17. A process according to claim 16 wherein the acid isselected from the group consisting of sulfuric acid, nitric acid andhydrochloric acid.
 18. A process according to claim 16 wherein the acidis sulfuric acid.
 19. A process according to claim 18 wherein theconcentration of the acid solution is from about 0.2 normal to about 3.0normal and wherein the amount of acid solution is from about 2% to 15%by weight based on the dry filteraid weight.
 20. A process according toclaim 16 further including the step of drying the filteraids aftercontact with the acid solution.
 21. A process according to claim 16wherein the starting diatomaceous earth filteraids have a beer-solubleiron content of less than about 50 parts per million or 0.005%.
 22. Aprocess according to claim 15 wherein the aqueous acid solution is mixedand maintained in contact with the diatomaceous earth filteraids at roomtemperature.